This study will determine the variability of the frequency and severity of obstructive sleep apnea in children as measured by two polysomnograms performed no more than 4 weeks apart. Children who present to the outpatient clinic with symptoms of sleep-disordered breathing sufficiently severe to clinically warrant an overnight polysomnogram will be asked to participate. The investigators will be blinded as to the scoring and interpretation of the polysomnograms. The initial polysomnograms have been scored and the appropriate clinical management rendered in all 17 patients recruited thus far. Preliminary data analysis comparing the second polysomnogram will be obtained after thirty patients are recruited. The variability measured will be a composite of the physiologic variability within individuals, the polysomnographic signal-quality variability, and the polysomnographic scoring variability. Data from this study will help to better characterize respiratory disturbance during sleep in children, and are critical to the interpretation of future studies examining the natural history of OSA and the efficacy of treatment.